This application relates generally to optical communication systems and, more particularly, to a system and method for transmitting and restoring optical signals.
A conventional method for transmitting optical signals is disclosed in U.S. Pat. No. 5,933,258 by Flanagan et al. This conventional method utilizes terminals, at a node, that multiplex fine granularity signals (such as STM-1, OC-12, etc.) from SONET, SDH, or other transport protocols, into coarse granularity signals (such as STM-16, OC-192, etc.) that are forwarded to an optical cross connect (OXC) switch. The signals are then transmitted to a terminal at another node in the optical communication system. In order for the signal to reach the terminal, it may have to be amplified or regenerated. The regenerator, at the OXC switch, converts optical signals into the electrical domain, performs various actions on the signals such as, for example, re-synchronizing the signal with the stratum clock, and then reconverts and re-amplifies the signals back into the optical domain. Furthermore, wavelength detectors are utilized at the regenerator to ensure the correct signal is always being transmitted for a particular route.
Such prior art approaches have a number of limitations. One such limitation is that a wavelength detection scheme must be implemented at all regeneration sites to ensure a proper reception of protection signals. The proper reception of the protection signals is needed to ensure that wavelength contingency (which is caused when a wavelength travels in an incorrect direction around the optical ring, from, for example, a link cut) does not occur. Additionally, optical signals incur significant power loss as they transit through the optical switching fabric at transit nodes or origination and destination nodes.
Further, as data centric switching products (such as routers and Asynchronous Transfer Mode (ATM) switches) emerge, the SONET interfaces from such products will increase in speed (e.g., from OC-48 to OC-192). This will lead to an inefficient handling of the optical signal traffic because the conventional interfaces (or tributary access) on SONET/SDH multiplexing equipment typically accept only low speed traffic (such as STM-1, OC-12, etc.). This traffic must then be multiplexed to create a high enough bit rate to justify long distance optical transmission thereby introducing a further limitation.
Another limitation of the prior art regards the fact that the conventional optical ring must be balanced by including the same number of working channels and protection channels between each node. Certain nodes, however, may not need as many working channels and protection channels as other nodes might because, for example, the traffic between these nodes may not be as heavy as the traffic between the other nodes. As such, the conventional optical ring may utilize a higher number of terminals than needed increasing the cost and complexity of the system.
Therefore, an improved system and method for transmitting and restoring an optical signal is desired to reduce or eliminate these limitations and design complexities.
In response to these and other limitations, provided herein is a unique system and method for transmitting and restoring an optical signal in an optical ring. The optical ring includes nodes, each containing an optical cross connect switching fabric that is coupled to a data switch. The optical cross connect switching fabric and the data switch are further coupled to a short reach side of at least one wavelength translation device and a long reach side of the wavelength translation device is coupled to a dense wave division multiplex (DWDM) coupler. The optical cross connect switching fabric and the data switch include at least one protect channel and at least one working channel for transporting the optical signal.
In one embodiment, the wavelength translation device receives the optical signal at a high speed rate, where the optical signal is a short reach optical signal and originates from a high speed interface on the data switch. The wavelength translation device then maps the short reach optical signal into a long reach DWDM optical signal at the high speed rate and forwards, via the DWDM coupler, the long reach optical signal to an adjacent DWDM coupler located at an adjacent node.
In some embodiments, if the long reach optical signal requires amplification between the nodes, the optical amplifier amplifies the long reach optical signal, where the optical amplifier is coupled between the plurality of nodes (for example, to the DWDM coupler and to the adjacent DWDM coupler).
In some embodiments, if the long reach optical signal requires improved signal quality, a regenerator regenerates the long reach optical signal, where regenerator is coupled between the plurality of nodes
In some embodiments, if a failure occurs on a link transporting the working channel, the protect channel is utilized to transport the optical signal.
In some embodiments, if the failure has recovered, the working channel is utilized.
In some embodiments, if the failure has not recovered and the protect channel is not available, optical cross connect switching fabrics at adjacent nodes on each side of the failed link switch the optical signal to an alternate diverse protect port.
In some embodiments, an optical pass through of the switched optical signal is configured between any transit nodes in the optical ring.
In some embodiments, if the failure has recovered, switching the optical signal back to the working channel.
These advantages, as well as others which will become apparent, are described in greater detail with respect to the drawings and the following disclosure.